The inventive subject matter relates to circuit interruption devices and methods of operating the same and, more particularly, to circuit interrupters providing a reduced-arc trip mode and methods of operating the same.
Circuit breakers are commonly used to protect circuitry, such as distribution wiring, from overheating due to short circuits or overloads. Circuit breakers typically include at least one set of contacts that is configured to be opened and closed by an actuator mechanism. The actuator mechanism is typically configured open and close the contacts in response to a manual or other mechanical input (e.g., by movement of a motorized actuator), and is further configured to rapidly open in response to an input from a trip unit.
Circuit breaker trip units may operate in a number of ways. For example, trip units for thermal magnetic breakers typically trip breaker contacts in response to current in and temperature of conductors in the breaker. Such trip units may use current transformers to sense currents for so-called “instantaneous” current-level tripping, and may use mechanical and/or electromechanical devices to provide thermal tripping.
Some circuit breakers provide adjustable instantaneous current settings wherein the current at level at which the breaker trips may be manually adjusted using a selector switch or similar device. Such adjustability may be desirable to prevent unwanted tripping due to, for example, momentary inrush currents produced by large motors or other equipment. An example of a molded case circuit breaker (MCCB) providing adjustable instantaneous tripping is described in U.S. Patent Application Publication No. 2009/0195337 to Carlino et al.
In some applications it may be desirable to place a circuit breaker into a maintenance mode in which closure of the breaker into a fault will result in minimized arc energy. For example, in some mining environments, it is a common practice to reclose a tripped breaker to determine whether a fault on the circuit has been cleared. Closure into a fault at a high instantaneous trip setting may result in significant arc flash. Operating the circuit breaker in a maintenance mode wherein the instantaneous trip setting is placed into a relatively low trip current level can reduce this risk. U.S. Pat. No. 8,508,891 to Carlino et al. describes a circuit breaker having an arc reduction maintenance mode that can be commanded from an external source.